Conventionally, scum generated on the water surface of a settling basin is removed by a scum removing apparatus provided on the downstream side of the settling basin. As shown in FIG. 4 of Japanese Patent Application Publication Laid-open No. Hei 9-19682, for example, a scum removing apparatus, which includes a tubular scum discharging mechanism constituted by a pipe having an axial center direction parallel to the water surface, including a slender opening in the axial center direction (longitudinal direction), and the pipe can rotate with the axis as a center, wherein that pipe is rotated at the time of discharging scum such that a part of the opening is positioned below water so as to introduce the scum into the pipe from the opening and discharge it, is well-known as such a scum removing apparatus. In addition, as disclosed in FIG. 1 of Japanese Patent Application Publication Laid-open No. Hoi 9-19682 and Japanese Patent Application Publication Laid-open No. 2000-202436, a scum removing apparatus, which is constituted by a trough including a vertically moving inflow floodgate, wherein the top end of the inflow floodgate of the trough is positioned below water at the time of discharging scum so as to introduce the scum into the trough via the inflow floodgate and discharge it, is also well-known.
However, the conventional scum removing apparatuses have shortcomings in that while scum near the opening and the inflow floodgate flows into the trough immediately after the pipe opening and the trough inflow floodgate are positioned below water, marginal scum flows into the pipe and trough thereafter together with a large quantity of water, requiring a long time for removing all of the scum, and thereby requiring a large quantity of water for removing the scum as a result.
More specifically, there are shortcomings in that since the scum generating and floating on the water surface takes on a single large plate shape with a constant thickness, hardness, and adherence (adhesion), a side of that plate-shaped scum adheres to the pipe and the trough and other sides respectively adhere to basin walls before the pipe or the trough operate. Therefore, while a part of the scum near the pipe and the inflow floodgate (trough) flows into the pipe via the opening and the inflow floodgate in sync with the operation of the pipe and the inflow floodgate, it is easy for only water to flow into the pipe and the trough thereafter, not allowing all of the scum to be removed in a short period of time. Moreover, when a large amount of water has flowed into the pipe and the trough, there is a shortcoming in that processing load of the scum processing equipment increases thereafter.
Furthermore, as disclosed in Japanese Patent Application Publication Laid-open No. Hei 9-276860, for example, the conventional scum removing apparatus also sprays pressured water at an oblique angle on top of the scum in order to provide locomotive faculty to move the scum toward the pipe or trough side in sync with movement of the pipe opening to below water or in sync with movement of the trough inflow floodgate to below water. However, the conventional scum discharging method of moving scum using only the flow of water has shortcomings in that electric power is consumed wastefully and power cost increases since only water flows into the pipe and the trough, this inflowing water is sent back to the settling basin, and the sent-back water is then pumped back up to the water treatment plant.
The applicant has already provided a scum removing apparatus in Japanese Patent No. 3943551 to solve the above-given shortcomings. The scum removing apparatus according to this patent (hereafter referred to as ‘patent apparatus’) allows the scum in the basin to smoothly flow into a scum inlet and effectively discharge the scum by smooth transfer of all of the scum.
In other words, the patent apparatus is a scum removing apparatus, which transfers generated scum on a current to the scum discharging mechanism side, and submerges a part of the scum inlet of the scum discharging mechanism under water at the time of discharging scum so as to remove the generated scum. The scum removing apparatus is characterized in that it is provided on the scum-flowing wall surface side of wall surfaces forming the scum inlet of the scum discharging mechanism, and a spraying means for spraying, for example, fluid (air) made of compressed air upward is provided along the wall surface.
Moreover, the patent apparatus is characterized in that it is also provided with a spraying means on the basin wall side in the water near the basin wall further upstream than the position at which the scum discharging mechanism is provided, wherein the spraying means sprays air upward along the basin wall. In addition, the patent apparatus is characterized in that it is provided with a water spraying means, which is provided further upstream than the position at which the scum discharging mechanism is provided, wherein the water spraying means sprays water obliquely downward on the scum discharging mechanism side to transfer the scum to the scum discharging mechanism side by the spraying pressure of the water.
The patent apparatus with the above configuration allows rapid discharge of scum since the scum may easily flow into the scum inlet and transfer of all of the scum can be performed smoothly. As a result, the patent apparatus may reduce amount of water flow accompanying scum discharge to 1/20 to 1/30 than by the conventional scum removing apparatus. As such, since the amount of water accompanying the scum to be discharged is far less than in the past, the patent apparatus has merits of reduction in equipment expenses for post-processing equipment such as a pressure flotation device, and reduction in power consumption of a lifting pump, thereby allowing contribution to energy conservation.
A verification test conducted at an actual certain sewage plant using the patent apparatus will be described. The scum removing apparatus provided with a tubular scum discharging mechanism used in this verification test has a 5 m-long pipe opening. When scum has grown to a thickness of 7 to 10 cm and to a length of 5 m further upstream from the pipe, the scum may be completely discharged by submerging a part of the pipe opening for 5 to 7 minutes. Moreover, in a verification test at another sewage plant, complete removal of scum by submerging a part of the pipe opening for 5 minutes every 24 hours and 5 minutes every 36 hours has been confirmed. As a result, the patent apparatus is given the nickname ‘Once-a-week boy’ since submerging a part of the pipe opening for approximately 10 minutes just once a week is sufficient, and has been introduced in the ‘Special Issue of Monthly Journal of Sewerage (P. 71)’ issued on Feb. 28, 2006.